Determining impurities in helium

ABSTRACT

Method and apparatus for determining the component impurities of helium. A sample of helium flowing in an analyzer system, including conduits having as a fixed part thereof a trap and coil assembly, is maintained at above atmospheric pressure and a rate of flow which allows its passage freely through the assembly being maintained at the temperature of liquid helium. Impurities are solidified and thereafter isolated by evacuation of the gaseous content of the assembly. The subsequent warming of the assembly provides a gaseous sample of the impurities for analysis in a mass spectrometer of the system. The direction of gaseous flow and the reading of data from instruments of the system are facilitated by valves distributed among the conduits, including a time controlled sampler valve. Liquid helium is maintained at a proper level with respect to the trap and coil assembly by an automatically controlled lift to which is fixed a Dewar vessel containing the liquid helium.

United States Patent Emerson et al.

[451 May 16,1972

[54] DETERMINING IMPURITIES IN HELIUM [72] lnventors: David E. Emerson;George W. Weems; Clarence A. Hoffman, all of Amarillo, Tex.

[73] Assignee: The United States of America as represented by theSecretary of the Interi- [22] Filed: Apr. 28, 1970 [21] App1.No.: 32,668

[52] US. Cl ..73/23,23/294, 55/267 [51] Int. Cl. ..G0ln 7/00, BOld 51/00[58] Field of Search ..73/l9, 23, 25, 28, 29, 17,

73/17 A, 15, 304, 304 C, 401; 23/294, 273 SP, 254; 137/392; 62/22;55/267, 268, 269, 66

[56] References Cited UNITED STATES PATENTS 3,291,980 12/1966 Coates ea1 ..73/23.1 X 3,557,604 l/l971 Baecklund.... ..73/19 3,194,054 7/1965Deaton et al. ..73/25 3,427,863 2/1969 Schultz 73/19 X 3,495,438 2/1970Mangum ..73/19 Frost ..73/23 Schwien 73/401 Primary Examiner-Richard C.Queisser Assistant Examiner-Ellis J. Koch AnomeyEmest S. Cohen andGersten Sadowsky [57] ABSTRACT Method and apparatus for determining thecomponent impurities. of helium. A sample of helium flowing inananalyzer system, including conduits having as a fixed part thereof atrap and coil assembly, is maintained at above atmospheric pressure anda rate of fiow which allows its passage freely through the assemblybeing maintained at the temperature of liquid helium. Impurities aresolidified and thereafter isolated by evacuation of the gaseous contentof the assembly. The subsequent warming of the assembly provides agaseous sample of the impurities for analysis in a mass spectrometer ofthe system. The direction of gaseous flow and the reading of data frominstruments of the system are facilitated by valves distributed amongthe conduits, including a' time controlled sampler valve. Liquid heliumismaintained at a proper level with respect to the trap and coilassembly by an automatically controlled lift to which is fixed a Dewarvessel containing the liquid helium.

2 Claims, 3 Drawing Figures PATENTEDMAY 16 I972 3, 662.588

sum 1 0F 2 //v VENTORS DA V/D E EMERSON I CLARENCE A. HOFFMAN GEORGE W.WEEMS DETERMINING IMPURITIES IN HELIUM mination of impurities in heliumin the part per billion range.

Analysis of helium impurities has heretofore been conducted byconcentrating the impurities on activated characoal held at 196C, andsubsequently separating these impurities on a 5A molecular sieve fordetection by a thermal conductivity type details of a controller forpositioning a vessel so as adjust the liquid helium level therein withrespect to a trap structure in which impurities are separated fromhelium.

The ipvention employs a mass spectrometer to determine I the parts permillion of contaminant components in a sample of helium. Basicconsiderations in an analysis of gaseous mixtures by mass spectrometers,such as pertains to the invention 1 disclosed herein, are discussed indetail in chapter IV of the text Mass Spectrometry by A. J. B.Robertson, published by John Wiley & Sons, Inc. New York, in 1954. Massspectrome- 1 of detector. Gas chromatography has also been applied forthe 5 analysis of such impurities with or without prior concentrationthereof. However, since a chromatographic procedure must be calibrated,some unknown or unexpected impurity could escape detection by beingretained in the column or being eluted simultaneously with anothercomponent. w

A helium testing method employing a preconcentration of impurities,implemented by freezing them at below atmospheric pressure, which isdescribed in US. Pat. No. 3,194,054, granted July 13, 1965, to W. M.Deaton and C. G. Kirkland, provides a highly accurate determination oftrace impurities, having a sensitivity of approximately 1 part permillion for each contaminant. Preparatory determinations required inconnection with this patented procedure increases the expense and timeinvolved in testing. Each use of the procedure requires that the volumeof metal coil and trap assemblies, and a trap-to-spectrometer pressurecorrection factor be determined along with time consuming calculationsbased on total sample pressure. On the other hand, the method andapparatus of the present invention permits a lower minimum detectablelimit of 0.01 part per million; and in repeated use does not requiredeterminations of total pressure, pressure correction factor, andspecific volume of the coil and trap assemblies. Thus, calculations areless complex, and are less time consuming. Moreover, the inventiondisclosed herein utilizes only one metal coil and trap assemblyconnected permanently to the apparatus whereby possible aircontamination, such as would be due to the connecting and disconnectingof metal coil and trap assemblies required fortesting according to theaforesaid patented procedure, iseliminated. Resultant savings of set-uptime made possible thereby permit significantly more analyses to be'madeduring scheduled use of the instant invention.

1n the present invention a sample of helium gas to be tested is passedthrough a trap and coil assembly held at the temperature of liquidhelium, and this gaseous flow is maintained at a sufficient rate toavoid the liquification of the helium in the sample. After evacuation ofpassages arranged between the coil and trap assembly and a massspectrometer, the solidified impurities are brought to room temperaturesuch that their gases expand into such passages and are disposed therebyto be routed into the mass spectrometer for analysis. The peak heightsestablished for the component impurities permit a determination of theirpartial pressures and part per million in the sample. The inventionfurther provides apparatus automatically determining the sample volumeof gaseous flow, and maintaining the trap and coil assembly in asufficient depth of 1 liquid helium during the passage of the sampletherein.

Objects and advantages of the invention will be more clearly understoodfrom the following description of a preferred procedure and embodimentof the invention, considered together with the accompanying drawingwherein:

FIG. I, is a schematic diagram showing an overall arrangement ofequipment for a preferred embodiment of the invention,

FIG. 2, is a schematic circuit diagram of a valve controller mechanismhaving utility in the arrangement of FIG. 1, and

FIG. 3, is a further schematic circuit diagram illustrating tersensitivities are determined by analyzing pure gases. An examplary massspectrometer analysis giving the sensitivities thereof to gases ofinterest appears in Table l which follows.

TABLE I Mass spectrometer sensitivities (20.0 microamperes ionizingcurrent) Component Sensitivity divisions/micron Hydrogen 400.34 Methane216.02 Neon 73.04 Nitrogen 199.93 Carbon Monoxide 209.12 Ethane 56.21Oxygen 150.60 Argon 210.63 Carbon Dioxide 159.00

Since these sensitivities normally vary slightly from one period ofspectrometer use to another, corrections for such slight variations aremade fron an analysis of a neon calibration gas each such operatingperiod and used as a base to ratio the other sensitivies for thatperiod.

It is known that partial pressure of each contaminant is determinable bydividing the mass spectrometer peak height reading for the component byby its sensitivity value as shown in equation 1).

partial pressure (p) =peak height (divisions)/sensitivitydivisions/micron l Also recognized is that when analyzing a sample bymass spectrometry, the partial pressure of a component in a gas mixtureis independent of the total pressure as long as the inlet system of theinstrument is at low pressure and the flow of gas molucules through thegold leak thereof at a constant rate is molecular. Therefore, thecontaminants in the sample are calculatable from the relationship.

P V /P, V, X 10 parts per million of component in sample. where P,barometric pressure, mm Hg V, volume of gas passed through apparatus, inliters P partial pressure in mm Hg volume of the mass spectrometer inletsystem and attached apparatus, in liters. V, calibrated internal volumeof the mass spectrometer inlet system and attached apparatus, in liters.

Sensitivity )K=ppm of component 11'] sample.

A system structured according to the schematic representation of FIG. 1,is particularly suited for facilitating mass spectrometer readings ofpeak heights, corresponding to contaminant components, which would beapplicable to the solution of the aforesaid relationship..Helium samplesare provided from a storage cylinder 10 to an outlet conduit 12 by wayof a manually operable cylinder valve 14. Cylinder 10 is associated witha pressure purge and safety pressure relief system 16 by way of a flowcontrol valve 18, and connections through conduits 20, and 21. Purge andrelief system 16 comprises a l microns filter 24, a purge volumecontainer 25 connected through conduits 26 and 27, with a low pressure16 psig) relief valve 28 leading to an inlet of container 25having atits outlet a high pressure (50 psig) valve 29. Cylinder furthercooperates with a trap and coil fixture 32 and valves 34 and 35associated therewith, by way of a remotely controlled sampling valve 37and connections through conduits 38 and 39. Valve 37 is solenoidoperated in response to switching operations in a controller mechanism40, to be hereinafter more fully described.

Trap and coil fixture 32 comprises a reservoir enclosure or trap 42which is entered at its top by a straight leg conduit 43, and at itsside by the end of a coil of tubing 44, and is otherwise constructed ina manner more fully shown and described in previously identified patentto Deaton et al. An arrangement of instrumentation 50, appearing in FIG.1, provides the system illustrated therein with means for measuring thevolume and pressure characterizing the sample flow through trap and coilfixture 32. This arrangement includes a gas flow indicator 52 to whichgas from fixture 32 flows by way of trap leg 43, valve 35, a conduit 54,a shut-off valve 56, a conduit 57, a low pressure (A psig) relief valve58, and a conduit 59. A wet test meter 62 is linked to flow indicator 52by way of a tubing 53 having operable therein an adjustable restrictor55 used in the calibration of the meter. Gas fed to meter 62 passesthrough in discrete quantities which are measured therein to providereadings of flow volume. Pressure-readings of gas flow from fixture 32are taken on a micromanometer 66 in a gas flow circuit including aconduit 67 extending back to I the fixture by way of valve 35, a valve69 adapted to isolate a mass spectrometer 70, as will be hereinaftermore fully explained, and further conduits 72 and 73. Micromanometer 66comprises an AC bridge circuit having in one arm a capacitor unitsensitive to the pressure of gas fed thereto, and in another arm a nullcontrol unit settable to balance the bridge and provide an. indicationof the gas pressure. A vacuum pump 75, connected to micromanometer 66 byway of a vacuum valve 76, and conduits 77 and 78, is also connected tofixture 32 by way of valves 35 and 69, as well as conduits 67, 72, aconduit 79, and a further vacuum valve 81. A vacuum gage 82 is connectedto pump 75 by way of conduits 84, 85, and valve 81. The passage definedby conduits 72, 79, 85, 84, and a further conduit 86, terminates in anexpansion volume enclosure 88. Mass spectrometer analyzer 70 isoperatively associated with fixture 32, and the instrumentation ofarrangement 50, by way of an analyzer valve 90 and a conduit 91 to theanalyzer, and conduit 92 to system conduits 72 and 79.

Referring now to the FIG. 2 showing of the electrical parts constitutingsample valve controller 40, sample valve 37 appears as actuatable by asolenoid represented by coil 96. Power for energizing coil 96, as wellas a timer motor 98, is

received from a 60 cycle source 100 on leads 101 and 102. A

step-down transfonner 104 is shown energized by voltage applied to itsprimary winding through leads 106 and 107 which are arranged to beconnected with power leads 101 and 102, respectively. The transformer isthereby adapted to supply voltageto a full wave bridge rectifier 110having valve actuator coil 96 connected across the output terminalsthereof.

Timer motor 98 is supplied with current on leads 112 and 113, the latterlead being directly connected to power lead 102.

Manual control of sample valve 37 is facilitated by a double pole,doublethrow switch 116 in a first positioning thereof which completes atits contact 118 an energizing circuit for transfonner 104 comprisingleads 101, 103, 106, 107 and 102. In a second positioning of switch 116circuits which are extended through contacts 120 and 122 thereof, areadapted to effect automatic energization of timer motor 98 together withtransformer 104 and valve actuator coil 96 therewith.

Accordingly, with switch 116 in its second position, an automaticoperation of controller 40 is initiated by depression of a self-releasedstart cycle button switch which completes across its contacts anenergizingcircuit for motor 98. This circuit from power lead 101 istraceable through lead 103, contact 120, leads 132 and 133, closedswitch 130, leads 134, 106, 136, contact 122, lead 112, timer motor 98,and leads 113 and 102. The timer motor is thus operated to rotate anotched camming disk 140, connected thereto, on which rides an actuatorfor a single pole, double throw switch 142. When the switch actuatorrides out of the notch in disk it shifts the single contact arm ofswitch 142 from an open circuit contact 144 to a contact 146 inenergizing circuitry for valve coil 96, as well as motor 98. The coilcircuit is traceable from power lead 101 through lead 103, contact 120,lead 132, a lead 150, contact 146 of switch 142, a lead 152, and lead106 to transformer 104 and a circuit return through leads 107 and 102.The motor circuit is traceable from power lead 101, through lead 103,contact 120, leads 132, 150, contact 146, leads 152, 106, 136, contact122, lead 112, motor 98, and a circuit return through leads 113 and 102.Since circuit closure at switch contact 146 shunts the contacts closedby button switch 130, release of this switch finds controller 40operating to maintain sample valve 37 open until camming disk 140 Arequisite cooling of trap and coil fixture 32 in accordance with theinvention is accomplished by immersing the fixture in liquid heliumcontained in a Dewar vessel 160, as illustrated in FIG. 1. Thisimmersion, is implemented by the operation of a .motor driven jackmechanism 162 to which vessel is affixed so as to present a surface ofliquid helium therein to the bottom of the fixture. The level of thissurface with respect to fixture 32 is adjustable by manual and automaticcontrol exercised over the jack by a position controller 166. Alow-power, high gear ratio drive motor 168, operationally directed bycontroller 166, is arranged to turn a screw 169 which positions alifting clamp of a conventional scissors device which sets the level ofjack mechanism 162 in an obvious manner. Jack motor 168, which appearsin the midst of the electrical parts of controller 166 as schematicallyrepresented in FIG. 3, is supplied with energizing power originating inan AC source connected to a step down transformer 170 by a circuitcomprising leads 172 and 174, and a power switch 176. A first secondaryof transformer 170 provides a voltage acrossinput terminals of a fullwave bridge rectifier 178 which in turn supplies an energizing output inthe controller on positive lead 180 and negative lead 182. A manuallyoperable control is provided which comprises a multiple contact, doublethrow switch 184 wherein interconnected switch arms are manipulatabletogether by a linkage 186 for movement to the right or left, as viewedin FIG. 3, so as' to effect the completion of circuits energizing motor168 to raise or lower Dewar vessel 160, respectively. The aforesaidcircuits include further connections through multiple contacts of arelay 188 which comprises an electromagnet actuator 190 made operable ina manner and for a purpose to be hereinafter explained.

Relay 188 responds to power in its coil 190 by shifting its contact arms191, 192, and 193 from engagement with contacts 194, 195 and 196,respectively, into engagement with contacts 197, 198, and 199,respectively. When manual control 186 is set so as to raise jack 162,contact arms 201, 202, 203 and 204 of switch 184 engage fixed contacts206, 207, 208, and 209, respectively. A drive for lowering jack 162finds contact arms 201, 202, and 204 in engagement with contacts 212,213, 215. Corresponding energizing circuits for the motor armature 210are completed by switch 184 whether up or down drive is directed. Thus,the positive voltage on lead 180 is applied to motor armature 210through contact arm 203 in engagement with either fixed contact 208 or214 since a lead 216 joins the fixed contacts and extends a circuittherefrom to motor armature 210 by connection to leads 218 and 219. Thearmature circuited is completed by a return lead 220 which extends thecircuit to a connection with source negative lead 182.

On the other hand, circuit polarity is changeable at terminals 222 and223 of the motor field winding 224, in accordance with the directionalcontrol set by switch linkage 186. With contact arms 201 to 204 shiftedright to accomplish an up drive, an energizing circuit to motor fieldwinding 224 is traceable from tenninal 222 to source positive by way ofa lead 226, closed relay contacts 191 and 194, a lead 227, closed switchcontacts 201 and 206, a lead 228, and positive lead 180; and fromterminal 223 to source negative by way of a lead 230, normally closed upand down limit switches 232 and 233, a lead 236, closed relay contacts192 and 195, a lead 237, closed switch contacts 207 and 202, a lead 238,and negative lead 182. When contact arms 201 to 204 are shifted left toaccomplish a down drive, an energizing circuit to motor field winding224 is traceable from terminal 222 to source negative by way of lead226, closed relay contacts 191 and 194, lead 227, a lead 240, closedswitch contacts 213 and 202, lead 238, and negative lead 182; and fromterminal 223 to source positive by way of lead 230, limit switches 232and 233, lead 236, closed relay contacts 192 and 195, lead 237, a lead239, closed switch contacts 212 and 201, lead 228, and positive lead180.

Up drive travel can be directed automatically by the electrical responseof a liquid level sensor 250 which is attached to fixture 32, andordinarily located in an upper section of Dewar vessel 160, as shown inFIG. 1. Sensor 250 may be a low power carbon resistor which changes inresistance as the liquid helium level drops with respect to fixture 32.Referring again to FIG. 3, sensor 250 appears with connections to leads252 and 253 which extend into the circuits of a conventional high-gainoperational amplifier 260. Energizing voltage is supplied to amplifier260 from a further secondary winding of transformer 170 by way of afurther full wave bridge rectifier 262. Positive and negative voltagesource leads 264 and 266 from the rectifier are extended to connectionsin the amplifier by leads 268 and 270, respectively. A low power relay272 operatively responds to the amplifier voltage across leads 274 and276 connected to the relay actuating coil 278. With power switch 176closed, liquid level sensor 250 constitutes a normally closed switch inthe amplifier circuit until liquid helium contacts the sensor wherebythe critical rise in its resistivity effectively opens the amplifiercircuit. However, when the amplifier is operational, relay 272 isenergized, and its contact arm is held closed at a fixed contact 279 ina circuit connected across rectifier output leads 264 and 266 which isadapted to energize actuator coil 190 of the directional control relay188. Closure of a double throw control switch 280 at its contact 281completes the relay energizing circuit which is traceable from sourcepositive on leads 264, 274, a lead 283, coil 190, lead 284, switchcontact 281, lead 285, relay contact 279, and lead 286 to sourcenegative lead 266. Relay 190 then functions to shift its respectivecontact arms 191 to 193 into separate engagement with contacts 197 to199, and thereby complete circuits energizing motor armature 210 andfield winding 224 such that motor 168 engenders an upward drive.

The armature circuit is traceable from source positive on leads 180,228, 288, 291, closed relay contacts 193 and 199, and leads 218 and 219,and from source negative on leads 182 and 220. The motor controlcircuitry is traceable from field winding terminal 222, by way of lead226, relay contacts 191 and 197, a lead 288, and lead 180 to sourcepositive; and from field winding terminal 223, by way of lead 230, limitswitches 232 and 233, lead 236, relay contacts 192 and 198, a lead 289,lead 238, and lead 182 to source negative.

A helium analyzing procedure in accordance with the present invention isefiectuated by following the steps thereof which are hereinafter setforth with reference to the embodiment of the analyzing systempreviously described.

1. Attachment of cylinder 10 by securing its valve 14 to conduit 12,makes available a helium sample for analysis. Valve 37 is initiallyclosed along with valves 14 and 18 to prevent gas flow in the system.Valves 34, 56 and 69 are likewise closed to isolate coil and trapfixture 32, flow indicators 52 and 62, and mass spectrometer 70,respectively, from the sample intake structure. However, the systemsfurther valves 76, 81, 90, and 35, are then in open condition.

2. After valve 18 is opened relatively wide, purge system 16 is madeeffective by momentarily opening cylinder 14, three or four times,allowing the pressure to subside after each time valve 14 is opened. Gaspurged from source 10 passes, by way of valve 14, into conduit 12 andthrough valve 18, conduits 20, 21, filter 24, conduit 26 low pressurerelief valve 28, conduit 27, purge volume container 25, and out of thesystem through high pressure relief valve 29. Valve 14 is thereafteropened fully as valve 18 is being closed. Micron filter 24 functions topreclude foreign matter from getting on the seats of relief valves 28and 29.

. Controller 40 is manually operated to open valve 37, and togethertherewith valve 56 is opened to place flow meter indicator gage 52 andwet test gas volume meter 62 in action so as to respond to gas flow.

4. The trap and coil assembly constituting fixture 32 is admitted intothe system by gradually opening valve 34 so as to protect gage 52, untilthe valve is opened fully. Valve 18 is again opened to initiate flow ofthe helium sample, by way of conduits 20 and 38, open valve 37 conduit39, opened valve 34, coil and trap fixture 32, conduit 43, open valve35, conduit 54, opened valve 56, and conduit 59, until gage 52 indicatesa pressure of approximately 20 inches of water. Thereupon, trap 42 andcoil 44 are heated gently to flush out residual impurities, after whichthe assembly is cooled to room temperature. Valve 18 is subsequentlyreadjusted to moderate sample flow until gage 52 indicates only twelveinches of water In a preferred embodiment of the system an indication of20 inches of water indicates a flow of 1, em /min which is higher thannormal in order to facilitate flushing impurities out of the coil andtrap assembly. Normal sample flow is 820 em /min.

5. The trap and coil assembly is thereafter cut-off from the system byclosing valve 34, and then valve 35. The volume indicated by the readingon wet test meter 62, and the ambient barometric pressure are recordedfor reference. Trap 42 is precooled by the application of liquidnitrogen thereto in a manually positioned separate Dewar flask. Liquidhelium in Dewar vessel is thereafter brought into contact with thebottom of the trap and coil assembly by closing jack controller switch280 on to contact 281, or positioning switch 184 of this controller toraise the vessel to the requisite height. Using manual control at switch184, the vessel is further raised until the level of the liquid heliumis at the third coil of fixture 32.

6. Sample flow through the trap and coil assembly is started by openingvalves 34 and 35 simultaneously, and a timing of the flow is started byadjusting valve controller switch exits from the system through gage 52,and the gas outlet of meter 62. Freeze out of the impurities is causedto occur at above atmospheric pressure by balancing the heat input tokeep helium from liquifying in the trap and coil assembly. Consequently,the flow rate cannot be allowed to drop during the flow-through step.Jack controller 166 is also set for automatic operation at that time byagain effecting closure of switch 280 at contact 281, whereby the liquidlevel of helium will be maintained at the third coil of the trap andcoil assembly. After three liters of sample have passed through the trapand coil assembly controller 40, shown in FIG. 2, automaticallyfunctions in response to an operation by its motor drive whereinprearranged timer cam 140 is rotated until it permits the contactchangeover of controller switch 142 which efiects the closure of valve37. In the disclosed embodiment the motor operated cam is set to run for3 minutes and 40 seconds.

-. The flowmeter is again cut-off by closing valve 56, as

sample control valve 37 is once more closed. Dewar vessel 160 is liftedby a manual adjustment of switch 184 to the right, as seen in FIG. 3,until the liquid helium level is raised one-half inch further so as topreclude the possible loss of the sample when pumping off excess gaseoushelium in a subsequent step. Valve 90 is operated to close it, whereasvalve 81, leading to vacuum pump 75, is left opened. Thereafterinterconnecting valve 69 is gradually opened until the pressure, asindicated on vacuum gage 82, reaches a maximum value. The possibility oflosing the sample due to an abrupt pressure change is thus lessened.With valve 69 completely open, a ready control is maintained upon valve35 so as to permit closure thereof when the pressure on gage 82 isindicated to be 50 microns. The wet test meter reading is recorded atthat time so as to establish a reading of volume of helium passed priorto the start of sample gas flow to which the reading taken at thetermination of gas flow through the apparatus is compared in order todetermine the volume of gas passed through the system, corresponding toV of equation (3), supra. Since the gaseous content of the system hasthen been removed by vacuum pump 75, only the solidified part of thesample remains in the trap and coil assembly.

. Liquid helium level position control 166 is again operated by manualcontrol switch 184 to lower the liquid helium level away from the trapand coil assembly. Valve 90, controlling the passage to massspectrometer analyzer 70, is opened momentarily for further evacuation,in particular, the area between the analyzer gold leak and the valve.Unheated air is applied to the trap and coil assembly so as to warm theassembly to room temperature. At this point in the procedure the gaseouscontaminants are to be expanded into the high vacuum (1 micron)associated with an expansion thereof into volume enclosure 88 and alliedconduit. Thus, valve 90 is closed to avoid a continuous leak through thegold leak into the high vacuum of the analyzer section of massspectrometer 70, and permit the sample to equilibrate. Accordingly,after isolating the analyzer 70 and pump 75 by closing valves 90 and 81,the

trap and coil outlet valve 35 is opened whereby the con-- tents of thetrap and coil fill the passages defined by the system conduits shut-offby the closed valves 34, 56, 81, 90, and micromanometer 66.

. After the pressure has equilibrated, valve 69 may be optionally closedto isolate analyzer 70 from the trap and coil assembly since it has noeffect on the analyses, and valve 90 is subsequently opened to admit asample from the contents of the conduit passages at the left of valve 69as seen in FIG. 1, to mass spectrometer for an analysis thereof. Eachindividual peak height established on spectrometer 70 detennines thepartial pressure of each component in the sample. The summation of theseindividual pressures should equal the total sample pressure as obtainedwith micromanometer 66. Valve 76 can be closed to prevent contaminationof the micromanometer pressure sensitive capacitor gage due toaccidental loss of vacuum or other means of contamination.

While a particular preferred procedure and an embodiment of the presentinvention have been illustrated and described herein, it will beunderstood that this invention is not limited thereto, but issusceptible to change in form and detail.

What is claimed is: 1. An analyzing apparatus for determining thecomponent impurities of a helium sample comprising means supplying saidhelium sample,

a gas trapping enclosure vessel,

a mass spectrometer analyzer,

a vacuum pump,

conduit means adapted to define a passage for the flow of said heliumsample from said supply means thereof to said enclosure vessel, havingvalve means connected therein to regulate the rate and volume of saidflow,

an insulated vessel supported at the base thereof by verticallyadjustable means, and storing liquid helium so as to present, when atfirst positions of adjustments, the liquid level of helium therein tothe base of said enclosure vessel, and at second positions ofadjustment, the liquid helium therein to outer surfaces of saidenclosure vessel, said vertically adjustable means comprising a platformhaving the base of said insulating vessel affixed thereto, amechanically adjustable means supporting said platform and operable toraise and lower said platform, a bidirectional motor adapted to drivesaid mechanically adjustable means, and a switching circuit enablingoperation of said motor in predetermined directions, said circuit havingswitch control means responsive to means for sensing the level of saidliquid helium in said insulated vessel which automatically conditionssaid switch control means into one state thereof whereby said circuitenables operation of said motor in one of said predetermined directions,and manually settable switch means made effective through circuitconnections made by said switch control means disposed into a secondstate thereof to condition said circuit to enable operation of saidmotor in either one of said predetermined directions, and

further conduit means adapted to define passages completed throughfurther valve means connected for operation therein in a predeterminedsequence whereby gaseous flow is selectively routed between saidenclosure vessel, said analyzer, said vacuum pump, and an arrangement ofinstrumentation including a gas flow indicator controlling a volumemeasuring meter, vacuum pressure gage, and a micromanometer measuringthe pressure of a gaseous sample produced in said enclosure vessel foradmission to said mass spectrometer analyzer.

2. A method for determining the component impurities of a sample ofhelium gas in parts per million comprising in sequence the steps offurther cooling a precooled gas trapping assembly, comprising anenclosure vessel and a predetermined length of a winding gas flowpassage entering said enclosure vessel, by initially displacing aconfined liquid helium bath so as to apply the liquid level surfacethereof to a base surface of said enclosure vessel, and subsequentlyfurther displacing said liquid helium bath so as to submerge saidenclosure vessel and a predetermined portion of said winding gas flowpassage within said liquid helium below said liquid level surfacethereof,

causing a measured volume of said sample of helium gas to flow by way ofsaid winding gas flow passage through said enclosure vessel cooled tothe temperature of liquid helium, and wherein the pressure is maintainedat an above atmospheric pressure and said flow of helium gas ismaintained at a rate which precludes the liquification of helium wherebyimpurities of said helium gas are solidified in said enclosure vessel,

still further displacing said liquid helium bath so as to furthersubmerge said enclosure vessel and said winding gas flow passage andsituate a predetermined additional portion of said winding gas flowpassage within said liquid helium below said liquid level surfacethereof, and thereafter evacuating the gaseous residue in said gastrapping assembly,

isolating said gas trapping assembly by shutting off inlet and outletconduits thereto, and thereafter yet still further displacing saidliquid helium bath so as to completely separate said liquid helium atsaid liquid level surface thereof from said gas trapping assembly,

warming said gas trapping assembly to an ambient temperature,

opening said outlet conduit whereby gaseous contents of said warmed gastrapping assembly is permitted to flow to a mass spectrometer analyzer,

determining the partial pressure of each component impurity asdetermined in said analyzer by the sensitivity of said analyzer withrespect to said component impurity,

and finding said parts per million of each of said component

2. A method for determining the component impurities of a sample ofhelium gas in parts per million comprising in sequence the steps offurther cooling a precooled gas trapping assembly, comprising anenclosure vessel and a predetermined length of a winding gas flowpassage entering said enclosure vessel, by initially displacing aconfined liquid helium bath so as to apply the liquid level surfacethereof to a base surface of said enclosure vessel, and subsequentlyfurther displacing said liquid helium bath so as to submerge saidenclosure vessel and a predetermined portion of said winding gas flowpassage within said liquid helium below said liquid level surfacethereof, causing a measured volume of said sample of helium gas to flowby way of said winding gas flow passage through said enclosure vesselcooled to the temperature of liquid helium, and wherein the pressure ismaintained at an above atmospheric pressure and said flow of helium gasis maintained at a rate which precludes the liquification of heliumwhereby impurities of said helium gas are solidified in said enclosurevessel, still further displacing said liquid helium bath so as tofurther submerge said enclosure vessel and said winding gas flow passageand situate a predetermined additional portion of said winding gas flowpassage within said liquid helium below said liquid level surfacethereof, and thereafter evacuating the gaseous residue in said gastrapping assembly, isolating said gas trapping assembly by shutting offinlet and outlet conduits thereto, and thereafter yet still furtherdisplacing said liquid helium bath so as to completely separate saidliquid helium at said liquid level surface thereof from said gastrapping assembly, warming said gas trapping assembly to an ambienttemperature, opening said outlet conduit whereby gaseous contents ofsaid warmed gas trapping assembly is permitted to flow to a massspectrometer analyzer, determining the partial pressure of eachcomponent impurity as determined in said analyzer by the sensitivity ofsaid analyzer with respect to said component impurity, and finding saidparts per million of each of said component impurities by multiplyingsaid component impurity partial pressure in millimeters of mercury by aconstant defined by V2/P1V1 X 106, where V is the volume in liters ofsaid gas flow through said gas trapping assembly, V2 is the internalvolume of said gas trapping assembly and condUits in which said gaseousimpurities are lead from said gas trapping assembly to said analyzer,and P1 is the ambient barometric pressure in millimeters of mercury.